Among the products generated in the steam cracking of hydrocarbons is a C.sub.5 stream. In many olefins units this stream is hydrotreated to remove dienes and acetylenes and then sold as a gasoline blending component. However, because of its low octane content, the C.sub.5 olefin/paraffin stream is of very low value. The stream can also be returned as feed to the olefin furnaces. The value as a feedstock in this application is also limited because the C.sub.5 olefins tend to crack to yield undesirable products. This invention is a process whereby the C.sub.5 olefins including cyclopentene are converted to more valuable products which do not boil in the C.sub.5 range. Thus the C.sub.5 paraffins can be isolated and used as feedstocks to the olefin furnaces.
It has long been known to contact various hydrocarbon fractions with acidic catalysts generally, and in particular, with siliceous acidic catalysts, including those referred to as crystalline aluminosilicate zeolites.
Zeolitic materials, both natural and synthetic, are many times known to have catalytic capabilities. Zeolitic materials typically are ordered porous crystalline aluminosilicates having a definite structure with cavities interconnected by channels. The cavities and channels throughout the crystalline material generally are uniform in size, allowing selective separation of hydrocarbons. Consequently, in many instances these materials are known in the art as "molecular sieves" and are used, in addition to selective adsorptive processes, for certain catalytic properties. The catalytic properties of these materials are affected to some extent by the size of the molecules which selectively penetrate the crystal structure, presumably to contact active catalytic sites within the ordered structure of these materials.
A wide variety of reactions have been carried out with zeolites including cracking, isomerization, hydrocracking, etc. Representative U.S. Patents disclosing and claiming contacting of various hydrocarbon fractions with crystalline aluminosilicates are U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,253; 3,140,322; 3,760,024; 3,894,102; 3,894,103; 3,894,104; 3,894,106; 3,907,663; 3,928,483; 4,012,455; and 4,150,062.
Boron is not considered a replacement for aluminum or silicon in a zeolitic composition. However, recently a new crystalline borosilicate molecular sieve AMS-1B with distinctive properties was disclosed in U.S. Pat. Nos. 4,268,420 and 4,269,813, incorporated by reference herein. According to these patents, AMS-1B can be synthesized by crystallizing a source of an oxide of silicon, an oxide of boron, an oxide of sodium, and an organic template compound such as a tetra-n-propyl ammonium salt. The process of this invention uses AMS-1B crystalline borosilicate molecular sieve.
The instant invention is concerned, not with hydrocarbons in general, but specifically with conversion of C.sub.5 olefins, namely pentenes and cyclopentenes, in a hydrocarbon stream comprising predominantly pentanes and pentenes, to C.sub.6 -C.sub.11 paraffins and olefins, aromatics and lighter olefins than pentenes. Additionally, the instant invention is concerned with recovery of the pentanes in the hydrocarbon stream as a desirable feed for steam cracking.
The formation of aromatic compounds from low molecular weight olefins is also known in the art but the selective formation of olefins from cyclopentenes and pentenes in the presence of pentanes wherein the pentanes are not converted to other hydrocarbons has not been previously known.